Changes:
- fixes many errors related to recurring events (I don't claim that everything is fixed, but the test cases I had now are OK)
- fixes crashes with events data parsing
- misc. bugs fixed
- progress bar is reset after each account processed (before it was stuck at 100% after the first account)
- stack traces after fatal (or mostly fatal) error are now reported in a gtk window instead of being dumped to the terminal. This will help greatly with debugging (you will be able to copy-paste the stack trace for debugging!), and also will remove the cases where Erminig hangs without giving any indication of why.